Evaporative media systems, for example direct evaporative coolers, are frequently used in commercial and industrial HVAC systems, including applications for data centers and power plant turbine inlet cooling. Evaporative media systems consume less energy than conventional cooling equipment and are increasingly being used to supplement and occasionally replace conventional cooling equipment. In operation, evaporative media systems use the enthalpy of vaporization of water as a means to cool and humidify air. Typically, this is accomplished by flowing air directly through a media wetted with water. As air passes through the wetted media, water evaporates by taking energy from the air to vaporize the water. Accordingly, the air temperature exiting the wetted media is reduced and the humidity is increased while the energy or enthalpy of the exiting air remains the same as the entering air. This type of a process is often referred to as adiabatic cooling.
Evaporative media systems typically use a water pump to transfer water in a tank below the media to the top of the media. The water flows down through the media where a portion of the water evaporates and the rest of the water drains out the media bottom into the tank below. The water continues to be re-circulated using the water pump, or re-circulation pump, with make-up water added to replace the evaporated water. Tank water is periodically drained and replaced with additional make-up water as the tank water concentrates to control and minimize scale fouling, biological fouling and corrosion.
Large commercial and industrial evaporative media systems usually have multiple cooling capacities to accommodate the varying cooling demands of the application. This is accomplished by wetting only portions, or stages, of the evaporative cooler media. There may be two or more stages on a single evaporative cooler with multiple cooling capacities. Typically, a single re-circulation pump is connected to a manifold with multiple staging valves and a water line to each stage. To wet a stage the staging valve is energized while the re-circulation pump is running, thus opening and sending water to that stage. Staging valves are opened and closed as needed to match the cooling demands of the application.
However, there are several problems with such single re-circulation pump and multiple staging valve designs. For example, staging valves can fail and are susceptible to plugging and/or sticking since they are a solenoid design and not a full port valve. Additionally, if the single re-circulation pump fails the evaporative cooler becomes inoperable. A single re-circulation pump is also necessarily oversized for much of the operating time which wastes electricity and heats the water. The pump must flow enough water to wet all the stages, however, it continues to pump at full power with fewer than all stages wetted. A further issue is that the staging valves must have a high flow rate and be suitable for wet environments, which makes them costly. When the large pump and manifold costs are added to the valves, the total cost can become excessive. Improvements are desired.